Steps to Configure Thunderbird with Office 365 Email :

• Open Thunderbird.
• Click the Thunderbird Menu icon (three horizontal bars) at the upper-right of the Thunderbird pane.

• Hover your cursor over Options and click Account Settings.

• Click Account Actions and then select Add Mail Account….
• Enter your name in the field labeled Your Name and enter your email address in the field labeled Email Address

• Enter your email password in the field labeled Password, and then click Continue. Configuration found at email provider will appear, but you have to click Manual Config.
  
  Please Note: Thunderbird will automatically try to set up the connection using default configurations, but you will need to click the Manual Config button to enter the correct configuration.

• For Incoming Server hostname enter outlook.office365.com, change Port to 993, change SSL to SSL/TLS and Authentication is Normal password.
• Enter smtp.office365.com in the Outgoing Server hostname field, change Port to 587, change SSL to STARTTLS and Authentication is Normal password.
• Enter your email address in the Incoming and Outgoing Username fields.

Click the Re-test button. You should get a message stating, “The following settings were found by probing the given server”.

• Click the Done button. Click OK to close the Account Settings window.

Thunderbird is now configured for use with your Office 365 email account.